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Answer:
3 times the smaller triangle base
Explanation:
The volume is proportional to the height and to the area of the base.
If the height is unchanged, the larger pyramid must have a triangular base with an area that is 9 times the smaller base area.
Since the bases are similar, the area ratio is the square of the side length ratio. The side lengths of the larger base triangle must be √9 = 3 times the side lengths of the smaller base triangle.